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Annette Walter, Michael Schuerer, Marina Bloj; Why do coloured filters improve vision?. Journal of Vision 2010;10(7):437. doi: https://doi.org/10.1167/10.7.437.
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Coloured filter media are said to improve colour contrast especially for sport related activities. The improvement is not well defined and apparently includes contrast vision (discrimination based on luminance differences), colour discrimination (the ability to distinguish colours in direct comparison depending on their colour distance) and some other effects like simultaneous contrast and adaptation. We developed an objective measurement method for detecting the effects of coloured filter media on colour perception while excluding the effects of luminance differences.
The apparatus employed in this investigation fulfils the requirements of “colorimetry by visual matching” and does not have the limitations of CRT or TFT displays. It is based on additive mixing of the emission spectra of seven different light emitting diode types (LEDs). Based on this, a freely adjustable spectrum is generated. The selected LEDs covered a continuous spectra in the range of 420 nm to 750 nm. In our initial measurements, the overall luminance level was fixed at 377 cd/m2. We evaluated just distinguishable colour difference on a vertically divided, two degree, test field around a yellow-green reference colour (CIEx=0,466, CIEy=0,453) along five colour directions. Measurements with volume filters (laser goggles (12 participants, 3 repeats), contact lenses (n=12, 3 repeats) and sport filters (n=3, 3 repeats)) were done in a similar fashion; the filters absorbed parts of the reference spectra and induced color shifts in different parts of the tri-stimulus space. Any induced luminance difference where eliminated by adjusting the LEDs' intensity.
For all filters and participants, the smallest colour discrimination ellipses (thresholds) were found in the yellow region, while size and geometry varied widely for each subject. We believe that this major improvement was based on increased colour discrimination in the yellow region and can not be accounted by variation in luminance or the use of a non-uniform colour space.
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